Climate Change Adaptation -- Coastal Risk Reduction and Resilience

Coastal areas are especially vulnerable to hazards, now and in the future, posed by waves and surges associated with sea level change and coastal storms. There are a variety of approaches that can be used to reduce the risks of these hazards to coastal areas, including natural or nature-based features (e.g., wetlands and dunes), nonstructural interventions (e.g., policies, building codes and emergency response such as early warning and evacuation plans), and structural interventions (e.g., seawalls and breakwaters). This topic is the subject of intense interest following Hurricane Sandy.

"Coastal Risk Reduction and Resilience: Using the Full Array of Measures," (pdf, 1.2 MB) a recently published paper, discusses the U.S. Army Corps of Engineers' capabilities to help reduce risks to coastal areas and improve resilience to coastal hazards through an integrated planning approach. Federal, state, local, non-governmental organization and private sector interests connected to our coastal communities possess a complementary set of authorities and capabilities for developing more integrated coastal systems. The effective implementation of an integrated approach to flood and coastal flood hazard mitigation relies on a collaborative, shared responsibility framework between Federal, state, and local agencies and the public.

"This report was prepared by a multidisciplinary team at the direction of the Directorate of Civil Works to clarify language used by the USACE to describe the full array of coastal risk reduction measures. This will help improve transparency and communications with our partners and stakeholders as we work together to address the increasing challenges posed by coastal storms and changing sea levels combined with aging infrastructure and a dynamic socioeconomic environment,"said Director of Civil Works Mr. Stephen L. Stockton.

The USACE approach to coastal risk reduction measures considers the engineering attributes of the various measures (how do these help reduce vulnerabilities) and dependencies among features (how do they impact each other) over both the short- and long-term. USACE also considers the full range of environmental and social benefits produced by component features of each measure.

As discussed in the report, there has been a renewed interest in coastal risk reduction efforts that integrate the use of natural and nature-based features. This renewed interest reveals the need for improved quantification of the value and performance of nature-based defenses for coastal risk reduction.

Natural features are created and evolve over time through the actions of physical, biological, geologic, and chemical processes operating in nature.

Nature-based features are those that may mimic characteristics of natural features but are created by human design, engineering, and construction to provide specific services such as coastal risk reduction.

Nature-based features are acted on by the same physical, biological, geologic, and chemical processes operating in nature, and as a result, they generally must be maintained in order to reliably provide the intended level of services.

Economic and Environmental Principles and Guidelines for Water and Related Land Resources Implementation Studies (U.S. Water Resources Council 1983) describes nonstructural measures as complete or partial alternatives to structural measures, including modifications in public policy, management practices, regulatory policy, and pricing policy.

Nonstructural measures essentially reduce the consequences of flooding, as compared to structural measures, which may also reduce the probability of flooding.

Nonstructural measures addressed by the USACE National Nonstructural Floodproofing Committee include structure acquisitions or relocations, flood proofing of structures, implementing flood warning systems, flood preparedness planning, establishment of land use regulations, development restrictions within the greatest flood hazard areas, and elevated development (Table 2 from the report).

Nonstructural measures can be blended well with the natural and nature-based features of the coastal environment, as well as with structural measures.

The purpose of levees, seawalls, and storm surge barrier gates is to reduce coastal flooding, while revetments, groins, and breakwaters are typically intended to reduce coastal erosion. All of these measures can reduce storm wave damage to some extent.